Validity of a strip theory - linear superposition approach to predicting probabilities of deck wetness for a fishing vessel

-- AUG. 197

ARCHEF

lepert No.

_CG-D-5-76

\/ALThITY OF A STRIP THEORY

_{LNER SUEPOSI1ION}

APPRCH TO PRED1TIN

_{PROBABILITIES F}

DECK 4ETNSS FOR A FISHING VESSEL

i4.

(, BALES

L1

E, PlOTTER

R,, M, 1,/ATKINS

I

4

FINAL REPORT

N'OVEMBER 197.5 O T4

Document is available to the public through the National Technical Information Service,

Springfield, Virginia 22161

Prepared for

DEPARTMENT OF TRANSPORTATION

UNITED STATES COAST GUARD

Off IC.

of l.s.ørch aNd

Dev.Iopm.nt

Wgshinjton, D.C. 20590

Lab.

v

Scheepsbouwkunde

Technische HogeschooF

Deift

/

e

2

3:

C,,

1 2 J4N 1976

The work reported herein was accomplished for the U. S. Coast Guard's Office of Research and Development, Marine Safety Technology Division, as part of its program in Commercial Vessel Safety.

The contents of this report reflect the views of N.. K. Bales, L. E. Motter, and R. M. Watkins of the David W. Taylor Naval Ship Res'earch and Development Center, Bethesda, Maryland, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views. or policy of the Coast Guard. This report does not constitute a standard, specification, or regulation.

.. D. NARKLE, J.

Captain, U. S. oast Guard Chief, Marine Safety Technology

Division

Of fice of Research and Development U. S. Coast Guard Headquarters Washington, D. C. 20590

Technical Report Documentation Page 1. Report.No.

--.CG-D-5-76

2. Government Accession No. 3. Recipients Catalog No.

4. Title and Subjille

Validity of a Strip Theory - Linear Superposition Approach to Predicting Probabilities of Deck Wetness for a Fishing Vessel

5. R& Date

November 1975 6. Performing Organization Code

8. Performing Organization Report No.

SPD-643-01

-7. Author's)

N. K. Bales, L. E.Motter, and R. M. Watkins

9. Performing Organization Name and Address

Ship Performance Department

David W. Taylor Naval Ship R&D Center Bethesda, Maryland 20084

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DOT-CG-50,646-B

13. _{Type of Report and Period Covered}

Final 12. _{Sponsoring Agency Name and Address}

United States Coast Guard 400 Seventh Street, S. W.

Washington, D. C. 20590 . 14. 'SponsorIng Agency Code

G-DST-2

15. Supplementary Notes - -

-The U. S. Coast (kiard Research and Development's technical representative for the work performed herein was .1. R. Amy.

16. Abstract

The motions and ship-to-wave relative motions of _{a fishing vessel in head,} regular waves are determined from a. model experiment and from _{strip theory} computations. _{The experimental results indicate that linear}

superposition is not universally applicable to the fishing vessel investigated. _Correlation between the experimental and strip theory results is _{never excellent, and} becomes extremely poor at the higher speed considered. _{The invalidity of} linear superposit.ion and strip theory found for the fishing _{vessel is shown} to produce gross errors in predicted deck wetness probabilities.

-17. Key WOrds -. Seakeep-ing . . Fishing Boats , Deck. Wetness . 18. Distribution Statement

. Document' -is available to the. public

through the National Technical Information Service, Springfield, Virginia 22161.

I9 Security Classif. (of this report) .

Unclassified

.

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

70

-ABSTRACT

TABLE OF CONTENTS

\ADMINISTRATIVE INFORMATION INTRODUCTION

VESSEL, OPERATING CONDITIONS, AND RESPONSES INVESTIGATED 2

STRIP THEORY COMPUTATIONS 3

EXPERIMENTAL CONSIDERATIONS

COMPARISON OF STRIP THEORY AND EXPERIMENTAL RESULTS . . DECK WETNESS PREDICTIONS

CONCLUSIONS

RECOMMENDAT I ONS

ACKNOWLEDGMENTS

APPENDIX A - EXPERIMENTAL FACILITY, APPARATUS, AND METHODOLOGY APPENDIX B - PROBABILITY OF DECK IMMERSION

APPENDIX C - FURTHER CONSIDERATIONS REGARDING RELATIVE MOTION REFERENCES

LIST OF TABLES

Table 1 - Ballast Conditions for the Fishing Vessel Table B1 - Deck Imersion Probability Data

LIST OF FIGURES

Figure 1 - Body Plan of Vessel Investigated Figure 2 - Profile of Vessel Investigated

III Page I. 9 11 11 12 13 15 19 25 28 29 30 31 32

Page

F1gre

3 - Pitch at 5 Knots 33

Fiqure l _{- Heave at 5 Knots} 34

FIgure ₅

-

Pitch-to-Wave and Heave-toWave Phases at 5 Knots 35

Figure 6 - Station 0.0 elative Motion at5Knots 36

Figure 7 - Station 1.0 RelatIve Motlon at 5 Knots 37

Figure 8 - Station

2.5

RelatIve Motion at 5 Knots 38

Figure 9 - Station 5.2 Relative Motion at 5 Knots 39

Figure 10 - Pitch at 10 Knots , 40

Figure 11 - Heave at 10 Knots 41

Figure 12 - Pitch-to-Wave and Heave-to-Wave Phases at 10 Knots 42

Figure 13 - Station 0.0 Relative Motion at 10 Knots 43

Figure 14

-

Station 1.0 Relative Motion at 10 Knots 44

Figure 15 - StatIon 2.5 Relative Motion at 10 Knots 45

Figure 16 - Station 5.2 Relative Motion at 10 Knots 46

Figure 17 - Pitch at 15 Knots 47

Figure 18 - Heave at 15 Knots 48

Figure 19 - Pitch-to-Wave and Heave-to-Wave Phases at 15 Knots 49

Figure 20 - Station 0.0 Relative Motion at 15 Knots 50

Figure 21 - Station 1.0 Relative Motion at 15 Knots 51

Figure 22 - Station 2.5 Relative Motion at 15 Knots 52

Figure 23 - Station 5.2 Relative Motion at 15 Knots 53

Figure

24A -

Calm Water Trim, Sinkage, and Wave Profile at 0 and

5Knots 54

Figure

24B -

Calm Water Trim, Sinkage, and Wave Profile at 10

and 15 Knots 55

Figure 25 - Pitch Amplitude Linearity 56

V

Page

FIgurt7 - R1.atLMbtIon Line

.1tiy at 5 Knots and AlL 1.5Q . . . 58

Figure 28 - Re)a1ve Motion L1neaIty at 10 Knots and /L = 1 75 . . 59

1jQf

29 Relative Motion Linearity at 15 Knots and AlL = 2.38 . . . 60 Figure 30 -. A&iative Motion Linearity at 10 Knots and

VL = 1.25

. . 61

vi

NOTATION

Freeboard in feet

Experimental value of F

F1 Theoretical value of F

ke Longitudinal radius of gyration In feet

I- Ship length between perpendiculars in feet

Distance from longitudinal center of buoyancy to a specified location In feet

P Probability of deck immersion per cycle of wave encounter Experimental value of P

Theoretical value of P

rA Single amplitude of ship-to-wave relative motion in feet

S Wave spectrum in feet2 seconds

T Draft (load waterline to bottom of keel) In feet

V Ship speed in knots

Single amplitude of heave In feet

20 Sinkage in feet

Salt water displacement in long tons

cZ. Heave-to-wave phase angle in degrees

C0 Pitch-to-wave phase angle in degrees

Single amplitude of'wave in feet Single amplitude of pitch In degrees Trim angle in degrees

A Wavelength in feet

Standard

deviation of shiptOwave relative motion

Experimental value

of a

Theretical v8lue of :

Wave frequency in radians/second

The motions and ship-towave relative motions of a fishing vessel in head,, regular waves are determined _{from a model experiment and from}

strip theory coiputations. The experimental results _{indicate that linear} super-position i _{not universally applicable to the fishing}

vessel investigated. Correlation between the experimental _{and strip therry results is never}

excellent nd becomes extremely poor at the highé4sged considered. _The

invalidity of linear superposition and strip theory foutt for the fishing

vessel is shown to produce gross errors in predicted deck _{s probabilities.}

ADMINISTRATIVE INFORMATION ABSTRACT

The work reported herein was sponsored by the

Fun1ng was spp1ied by _{Military Interdepartmental}

50646. _{At the David W Taylor Naval}

Ship Research work was identified as Work Unit 1-1568.014.

INTRODUCTION

Deck wetness is an especially critical problem for small, offshore work-boats, e.g., fishing vessels. _{Water on deck can have}

a negative effect on the stab1Iiy of such vessels, and _{their crews must frequently work}

on weather decks. _{Hence, the development of freeboard}

requirements for these vessels constitutes an important regulatory activity. _{Application of state-of-the-art} analytical techniques to predict _{probability of deck}

wetness as a functjon of freeboard and ship-to-wave relative motion would obviously provide an

expedi-ent

means of establishing freeboard requirements _{for fishing boats. However,} the analytical techniques involved _{require many assumptions;}

and little attention has been directed to validating _{these assumptions for fishing}

vesel.

United States Coast Guard. Purchase Request Z-70099-5-and Development Center, the

wavelengths encompassing, the associated resonant encounter frequencies. F\or experimental purposes, wave steepness was to be varied from 1/90 to 1/30 at each wavelength.

STRIP THEORY COMPUTATIONS

Strip theory computations for the vessel operating conditions,, and responses just described were performed at the start of the project so that they could be used to provide guidance in establishing a detailed plan for the experiment. DTNSRDC's Frank close-fit ship-motion ,coniputer program, YF '1 see reference 3, was.employed for the computations. YF 17 uses a modified version of the Korvin-Kroukovsky strip theory, reference 1, to compute the added mass and damping coefficients for each Ship station input to it. (The Korvin-Kroukovsky theory Was modified for the YF 17 program to include speed

correction terms, the most recent of'which was added to 'itch damping as (. _{documented. In reference..k.}

Input to the YF 17 program. consists of ship characteristics including

length, beam, draft and longitudinal radius of gyration as wel.l as.offsets for, a sufficient number of stations to adequately describe the hull form. For the fishing boat, a 13-station representation (Stations O0,

0.5, 1.0,

1.5,

2.0, 3.0, 4.0, .5.0,

6O, 7.0, 8.0, 9.0

and 10.0) was considered adequate.

Table 1 indicates that this representation did, in fact, produce a displacement within 0.5 percent of that specified by the USCG.

The results of the YF 17 computations, see Figures 3 through 23, proved

o be unusual in two respects. ' The transfer 'function peaks occurred at wave-length. to' ship length ratios on the order of

1.5

to 2.5 rather than In the 1.0 to _1.5 range typical of conventional ships, and the maximum' transfer functions were very large at the higher speeds. To illustrate the latter point, consider the' transfer function of pitch at 15 knots as presented by Figure ₁₇ The YF 17 results given by this figure 'indicate tha't the amplitude

of' pitch will reach 3.30 times wave slope. A pitch amplitude of 19.8 degrees (one way) is Implied for 1/30 steepness waves. ,,

As YF 17 has no history of failure to correctly locate transfer function peaks, the tendency of these variables to peak at unusul1y high wavelength to

ship length ratios could bera.IonalTzed in terms of the novel geometry of the fishing vessel. On the other hand, there were ground.s to view the large

transfer function magnitudes with suspicion. YF 17 was developed to predict the motions of cargo and military displacement vessels quite different from the fishing boat of concern here. For such hulls, YF 17 has been shown to. predict motions fairly well for Froude numbers as high as 0.4., For other hull designs, agreement between measured and predicted motions IS sometimes found

satisfactory only to a much lower Froude Number. The fishing boat differs greatly. n, hull form from the types of vessels for which YF 17 was developed; and the maximum speed at which it was evaluated, 15 knots, corresponds to a Frude number of 0.48.

It appeared that, should the YF 17-predicted transfer function peak magnitudes prove to. be correct, the model would not survive in the steeper waves planned for the experiment. Considering this factor in relationship to the lIkelihood of misprediction just discussed, it was decided to specify transducer calibration ranges for the experiment at considerably lower levels than implied by YF 17. Further,, to guard against the possibility that the YF 17 predlctions'df transfer function peak locations were incorrect, a plan which allowed considerable flexibility In wavelength selection during the experiment was adopted.

EXPERIMENTAL CONSIDERATIONS

A model representing the vessel depicted by Figures 1 and 2 at a scale ratio of. .11.16 was used for the experiment. A detailed description of the experimental facility, apparatus, and methodology employed Is given in

Appendix A to this report. Here It suffices to note that the model was

ballasted to the conditions del ineated by Table I, was.self-propelled, and was.

free to move In all degrees of' freedom while data were being collected. The experiment was conducted in head, regular waves of various lengths and steepness at prototype equivalent speeds' of 5, 10 and 15 kflots. 'Measured

responses were monitored' and compared with thea priori strip theory results to aid i establishing areas of major discrepancy. Several observations

relevant to the cOmparison were made during the experiment. To provide some perspective, these observations will be described before the basic.experi-mental data is presented and discussed. -.

The locations selected for evaluation of relative motion (StatIons 0.0,

1.0, 25'

and

5.2)

emphasized the bow region as is usual for invefrtlgatlons of

deck wetness in head waves. Contrary o the iinpl kit, a priori assumption, the experiment indicated that the fishing boat investigated was much more prone towetness amishlps and' aft than in the bow area. Fo'c'sle deck wetness

'occurredduring only two of the 178 runs made during the experiment.. In

con-trast, there was wetness amidships and aft during almost every run.;

Both Instances of fo'c'sle deck wetness occurred at 10 knots in waves of 1/30 steepness True bow submergence was not involved in either Instance Rather, the wetness resulted from distortion of the incident wave train by the model. The forepeak flcllppedu wave crests and threw sheets of'water onto

the fo'c'sle deck.

-Water on the after decks was usually shipped through the freeing ports The model was, of course, ballasted to a minimulm freebOard condition which was (in an absolute sense) especially marked aft of the fo'c'sle deck At speed, the model experienced sifikage and bow-up trim which further reduced freeboard aft At 10 and 15 knots, the trim and sinkage were sufficient to admit shipment of 'water through the freeing ports- even in calm water.

In waves, water was shipped through the freeing ports at all speeds. At 5 knts the wetness was minimal, but at 10 knots the main deck was usually awash, and there was some splashing onto the poop deck At 15 kiiots, water was shipped through only the after freeing ports, and main deck wetness was

less extensive than at 10 knots However, the general wetness fft of midship at ₁₅ knots was augmented by a heavy propeller wash which threw water over the fantail bulwark onto the poop deck

Another factor which should.be mentioned here is that the model generated an unusually prominent wave system when at speed. This wave system combined

with the incident waves to produce a complex wave field around the hull, It

appeared that the spatial characteristics of this field varied with incident wavelength as well as with speed. Surface turbulence was usually present within thecombined wave field, and caused difficulty in measuring relative motion when it occurred at a transducer location. Even In the absence--of

turbulence, it appeared likely that the vessel's Own wave system would influence its measured relative motions.

To provide some quantitative support for the foregoing discuss ions, fishing vessel measurements taken in calm water were examined to obtain trim, sinkage,and wave.profile.data. Video tapes of the calm water runs were viewed .to.cross-check the measured wave profile data, and notable discrepancies were

found to occur forward of Station 1 at 10 and 15 knots due to transverse van-ations in wave profile. -A wave profile aft of mjdships was also inferred from the video tapes, for the 15-knot condition, The results of this investigation are sumarized by Figures 24Aand 24B. Independent of the 10 and 15-knot dis-crepancles forward of Station 1, which will be discussed later, these results clearly indicate that the vessel's trim, squat, and wave system will effect its wetness characteristics.

Finally, It must be noted that, at least in the context of experiments with more conventional hulls, the 15-knot condition appeared to be unrealistic

because of deck wetness and inadequate propulsive capacity. As implied by the preceding discussion, the general impression given by the model at a prototype equivalent speed of 15 knots was that it was running with its after quarter

submerged. Further, the model propulsion system, though roUtinely used to drive models up to three times the size of the fishing boat model, appeared to be

heavily loaded even in very small waves.

USCG representatives were consulted with respect to this matter while the experiment was in progress, and felt that the 15-knot condition should be

pursued as àr as practical. This was done, -but it proved impossible to drtve the mqdel at this equivalent speed in long waves with a steepness exceeding 1/40. Under these conditions, breakers in the model propulsion circuitry started to throw, and gears in the drive train were ultimately stripped. So, while wave

.steepnesses.uptothe order of 1/30 were usually attaIned, the maximum steep-'nesses reached at 15 knots in lông waves were about 1/40.

Itis now in order to present the basic results of the fishing vessel ex-periment. This is done in Ftgures 3 through 23, All transfer functions and phase angles are in terms of fundamental frequency results as obtained via harmonic analysis of the recorded time histories. The variable ranges measured at each wavelength are indicated by capped, vertical bars whenever the complete wave steepness range (1/90 to 1/30 except at 15 knots In waves of more than

twice ship length, then 1/90 to 1/40) was evaluated. Individual points are shown for Wavelengths In which the 'complete steepness range was not evaluated.

The, variability associated with the measured transfer functions and phase angles of- pitch and heave is generally within the limits of experimental

accuracy for a linear or near-linear system. The measured relative motion transfer functions, on the other hand, exhibit an uncomonly great degree of variability. In this context, some difficulty associated with the measurement of relative motion (due to turbulence) has already been noted. However,

indications of nOnlinear behavior were alSo' observed during the experiment. At

both JO and 15 knots, the forward relative motion transfer' functions showed a strong tendency to' increase with wave steepness for wavelengths near the transfer function peaks.

To assess t:he possibility of nonlinear behavior, numerous plots of response versuswave amplitude at fixed wavelength and vessel speed were

constructed. Representative examples of these plots are presented in Figures 25 through 30. A linear interpretation has been made in these figures so that departures from linearity can be observed. All of the figures except the last apply-to wavelengths near the transfer function peak of the variable and speed

under consideration.

Itwas concluded that definite nonlinearitles existed in relative motion at Stations 0.0 and,i.0 at speeds of 10 and 15 knots of wavelengths near the -transfer function peaks of these variables, Further, the nature of these

nonlinearities issuch that the associated transfer functions will increase with Increasing wave height. All responses other than those just cited can be

The implication of the foregoing conclusion is that linear superposition 'Is nt un'iversall.y.appllcable to the fishing boat Investigated. In contrast to

more typical ship response nonli.nearltles, the results indicate that using linear surposition techniques with response amplitude operators obtained experimen-tally in low waves could underpredict responses in random waves The degree of underprediction involved for the particular case of deck wetness will be explored

subsequently.

An unusual.propertyof the measured relative motion transfer functions is that they do not always tend to unity at high encounter frequencies for which absolute ship motion tends to zero. This situation gives rise to questions as to the applicability of the state-of-the-art kinematic definition of relative motion to the fishing vessel under consideration. This definition assumes that

relative motion is the vector sum of absolute ship motion at a particular location and the incident wave at the same location. No allowance is made: for the ship's own' wave system or for disortion of the incident wave by the, ship.

It has been noted that the fishing vessel was observed to generate a heavy wave system,' and that this wave system combined with the incident wave.systern to

produce a complex. wave field in way of the model hull. So, it. appeared con-ceivable that the failure of the measured relative motion transfer functions to converge to unity might be attributable to inapplicability of the kinematic definition of these variables. This possibility was evaluated by using the kinematic definition to. compute relative motion transfer functions on the basis of faired values of measured pitch, heave, and phase relationships. The results of these computations are shown by the relative motion transfer function figures previously.'presented. They verify the initial hypothes-is, but give rise to new questions by virtue of the failure of the computed values to fall withifl the' measured range for wavelengths not associated with the conver,gence problem.

Some. of the discrepancies' between the measured.and computed relative motIon transfer fuñtions may be attributed to the methodology employed for the compu-tations. Performing these computations on a run-by-run basis rather than from faired data would have prov'ided a more definitive measure of the importance bf

the' discrepancies. ' In the absence of. such computations the possibility of a

general 'failure of the kinematic definition of relative motion must ,be admitted.

The fact that the vessel's own wave system is instrumental in causing this failure is evident from the fact that the differences between the _computed and measured transfer functions are largest when the measured _{motions of} the vessel are essentially nil1 i.e., in those cases where _{convergence to} unity is anticipated.

There is one other factor, again related to the vessel's own wave system and its Interaction with the Incident wave system, which could _{have contributed} to the discrepancies between the measured and computed relative motion transfer functions. _{When introducing Figures 24A and 24B, it was pointed out that video} tape and relative motion records of the experiment indicated different _wave profiles under some conditions. _{These differences are attributable to the fact}

that the wave profile deduced from the video tape was directly alongside the model hull while the relative motion transducers were, at model scale, _located

10 to 12 inches outboard of the local weather deck edge. _{(A location this far} outboard is required for operation of the transducers employed.) _{Hence, it}

is possible that the measured relative motion transfer _{functions do not} exactly define ship-to-wave relatiórnships immeiately alongside the model.

It should be noted that this possibility also constitutes _{a failure of the} kinematic definition of relative motion as distance outboard is _{not a parameter}

in the kinematic formulation.

COMPARISON OF STRIP THEORY AND EXPERIMENTAL RESULTS

In the context of the earlier discussion of the results of the strip theory computations, it Is evident from Figures 3 through _{23 that strip theory} did, in fact, greatly overpredict the _{responses of the fishing vessel at the} higher speeds ponsidered. On the other hand, the prediction of wavelengths at iich the transfr functiens woul4 peafr w

ppprcimat1y corrrct. Though

discrepancies in peak location are evident, th _{experimental peaks did occur} at unusually large wavelength to ship length ratios.

Agreement in all transfer functIordegenerated with vessel speed, _but the same did not hold true for phase angles. _{In fact, the heave-to-wave phase}

angles at 15 knots were among the better predictions. The accuracy of the relative motion predictions did not vary greatly with location.

Some perspective may be added to the foregoing discussion by noting that the agreement between the strip theory and experimental results for the fishing vessel at 5. knots would have been considered to be poor for 'a conventional cargo or naval hull.

There are numerous reasons for the failure of strip theory to accurately predict the responses of the fishing vessel. Geometry and maximum Froude number were, considered during the Initial discussion of the strip'theory results., 'Consideration of the exprlmental results'brought to light some nonlinear relative motion characteristics and showed that the State-of-the-art. kinematic definition of relative motion was not generally valid for the fishing boat. While the strip theory computations assume 11earityand'ernp1oy the kinematic definition of relativemotion,* ft is felt that the Invalidity of these 'assumptions played only a minor roll in producing the discrepancies found. If the nonlinearity and kinematic problems' had played the major role, the strip theory results would have'closely bounded the directly measured relative motions and/or those computed from measured pitch and heave. So, the basic difficulty'

lies with the strip theory computations of pitch and 'heave. .

State-of-the-art advances in basic hydrodynamics will likely be required before the seakeeping characteristics of such craft as the fishing vessel under consideration can be predicted 'accurately. However, one simple

cause for

the failure of the strip theory computations may be postulated. Strip theory does not account for trim and/or sinkage, i.e., the underwater body of a vessel, is.. assumed to have.the same characteristics when at-speed as when at rest. While.

this assumptfon is moderately accurate for large, conventional hulls, Figure 24B shows it to be grossly inaccurate for the, 'fishing vessel at 15 knots. Hence, it would be of considerable Interest to see if strip theory computations applicable to the vessel's dynamic waterline at 15 knots would, Improve, the existing, very poo.r correlation with, experiment.

*Strictly _{speaking, the relative motion computations are not performed via strip} theory. Rather, pitch and heave are computed from' strip theory, and these

predictions are used to compute' relative motion via the kinematic definition. See Appendix C for further discussion.

DECK WETNESS PREDICTIONS

since neither strip theory nor linear superposition are generally appli-cable to the vessel/operating condition/response matrix investigated, valid predictions of deck wetness probabilities can hardly be expected. However, t

was considered desirable to quantify the errors involved; and.to examine the pOssiility of obtaining useful bounds over some subset of the matrix investi-gated. This èxplorition was performed using the probability of deck Immersion formula given in reference 5, and is described in Appendix B. The results are not encouraging.

Freeboard errors alone can produce probability of immersion errors of as much as a factor of two. Even if Station 5.2 (where, the freeboard-induced

errors' were worst) is not considered, freeboard errors alone introduce lQ- to 40-percent errors in deck immersion probabilities. Strip theory errors alone

reduce averag deck immersion probability errors f a factor of two. At 15

knots, the avenìge strip theory-induced error is nearly a factor of four. Linear superposition errors alone can produce factor of two discrepancies In deck Immersion probability. Combining errors from the sources delineated above can result In errors approaching an order of magnitude in the probability of deck Immersion. On the other hand, fortuitous combinations of errors can make

the ultimate probability nearly correct.

It cn be observed that predicted probabilities of deck immersion agree better with experiment as ship speed decreases and as the probability of

immersion increases. However, no significant data base subsets admitting conservative (within, say, a factor of two) predictions Qf deck immersion

obabilIties

can be unequivocally defined. Hence, it must be concluded that

sttof-t-art analytical techniques are inadequate even to establish

engineering limits for the probability of deck wetness of the fishing vessel

invest 1g. ted.

CONCLUSIONS

Neither strip theory nor linear superps1tion is generally applicable to the fishing vessel investigated. Further, the state-of-the-art kinematic

definition of relative motion is not generally accurate for this vessel. The deficiencies associated with linear superposition and with the kinematic

definition of relative motion1; though per se significant, are minor in compari-son to the errors associated with strip theory.

Deck immersion probabilities computed asSuming that strip theory, linear superposition, and the kinematic definition of relative motion are valid can differ from experimentally based probabilities bynearly an order of magnitude. The nature of the discrepancies involved is sqch that vIable englneerin,g

estimates

of

deck Immersion probabilities cannot be obtained over any signifi-cn)s4Jbset of th' yesSel/operating condition/response matrix investigated

RECOMMENDAT I ONS

The deficiencies in the state-of-the-art kinematic definition of relative motion which were evident in the case of the fishing vessel can be expected to occur to a lesser degree for most hull forms.* Hence, a more, exhaustive

explorátio.flcf these deficiencies should enchance our capabilities in. analyzing relative motion phenomena in general. The fishing boat data would be particu l.arly'usefül In this context by' virtue of the fact that the phenomena in

question wereôf sufficient magnitude to be easily measured. Kinematic compu-tation of relative motion from measured pitch and heave and comparison of these results with measured relative motion data on a run-by-run basis is recommended as a reasonable first step.

It was suggested that some'of the differences found to exist between the strip theory and the experimental results for the fishing vessel might be.. attributed to' the considerable changes In the underwater body of the vessel, which occurred as a result of trim and squat at high speed. Accordingly,. It. Is

recommended that strip theory computations be performed 'for the fishing vessel at its 15-knot, dynamic waterline. The resultant predictions should then be compared with those obtained from the experiment to see If a significant

Improvement in correlation is obtained.

See Appendix

Pendln'g advances in the current state"of-the-art as regards ship motion and relative motion computation1. it Is recommended that fishing vessel deck wetness be harcterized on the basis of model experiments in random waves. In

this context It should be recalled that the fishing $at evaluated here exhibited more sverè wetness aft of midship than in the bow area. Hence,

future xpeririénts with similar models should be plannedto admit analysis of deck wetness any*here along the vessel's length. Some consideration of freeing

port design would also seem to be in order.

ACKNOWLEDGMENTS

Mr. W. Dixon and Mr. D. Huminik, both of DTNSRDC, were responsible for preparation and operation of the instrumentation system utilized for the fishing boat experiment. The use of so many ultrasonic transducers on such a mall model posed a number of unique problems which Messrs. Dixon and Huminik capably

resolved. Without confidence in the validity of their work, the novel results of this Investigation could not have been reported.

(Intentionally blank)

APPENDIX A

EXPERIMENTAL FACILITY, APPARATUS, AND METHODOLOGY

The USCG supplied a model of the fishing vessel shown in Figures 1 and 2 of the text for the experiment. This model, designated F-34, was built to a scale ratio of 11.16. It was of wooden lift construction to the fo'c'sle deck forward, the main deck amidships, and the poop deck aft. The bulwark around the working decks was modeled In sheet aluminum. Four freeing ports

penetrated the bulwark model at the main deck level on each side. An all-movable rudder with approximately 67 square inches of profile area was supplied with the model.

The experiment was to be performed In DTNSRDC's rectangular seakeeping basin. This basin Is 360 feet long by 240 feet wide, and has a water depth of 20 feet. Wavemakers are located along two, adjacent sides of the basin; and a bridge, which can be rotaed through 1e5degreearc to provide selected headings with respect to the wavemakers, spans the basin. A carriage to accommodate experimental equipment and personnel is suspended beneath the'-bridge and will, run its length at a preselected speed.

The instrumentation system for the fishing boat experiment was designed to measure, record and reduce data on model motions in all six degrees of f,eedom, relative motion at four locations, wave elevation, and carriage velocity. In

addition, it was to provide video records of the experiment via an indepdndent subsystem. As an auxiliary function, it was to employ the measureds

yaw signals to control the model rudder. Figure Al shows the esseW*tàl. of the Instrumentation system In flowchart form.

All angular displacement measurements were obtained from gyroscopic

transducers and all linear displacement measurements were obtained from ultra-sonic transducers. Carriage velocity was measured via a toothed gear and

magnetic pickup. Two video cameras were employed, and the special effects unit split the monitor screen allowing the views from both cameras to be seen

Model outfitting Involved Installation of propulsion and steering gear, transducer mounting, and taking measures to assure the watertight integrity - 'of the model.

A five horsepower electric propulsion motor was mounted inside the model shell and coupled to the propeller shaft using two, bevel-gear, right-angle drive units. Provision was made to obtain a readout of shaft revolutions via a toothed gear and magnetic pickup assembly. A stock DTNSRDC propeller 6.74 Inches in diameter with a pitch of 7.30 inches was employed. This propeller had four blades and was right-hand turning.

A rudder control servomechanism was mounted inside the model shell and linker to the rudder stock.

Gyroscopic transducers were mounted inside the model shell on its longi-tudinal centerline. The pitch/roll gyroscope was at the longitudinal center of buoyancy location. The yaw gyroscope was in way of the forward quarter point.

All ultrasonic transducers were mounted above deck level. The heave transducer was on-the longitudinal centerline at the longitudinal center of buoyancy location. The sway transducer was at the longitudinal center of buoyancy location, but to port of the centerline. The surge transducer was on the centerline at the stern. Cantilever brackets suspended the relative motion transducers 10 to 12 inches outboard of the local weather deck edge at Stations 0.0, hO, 2.5 and 5.2 (the longitudinal center of buoyancy location).

The model was

fully

decked to ensure its watertight integrity. The decking incorporated a well amidships to draw cables from the Interior running gear and transducers. This well was protected by a spray shield located in way of the after edge àf the fo'c'sle deck.

Attachment of the aluminum bulwark completed the outfitting effort, and readied the model for ballasting.

To ballast the model, weights were first added as required to obtain the desired draft and displacement. Displacement was taken to be the controlling parameter since there was some ambiguity (about + 0.25 inches) associated with establishing draft marks on the model. After the desired draft and displacement

were attained, the model was oscillated in air as a Bif liar pendulum to obtain the desired longitudinal radius of gyration by longitudinal movement of the added weight. Table 1 of the text gives the results of the ballast ing pro-cedure. This table also gives confirmation data obtained after the experi-ment.

Finally, the instrumentation system was placed aboard the carriage; and the outfitted and bal lasted model was attached to the carriage by restraint ropes, safety ropes, and umbilical instrumentation nd power cables. Targets for the ultrasOnic heave, sway and surge transducers ware attached to the carriage as ware the video cameras and requisite lihting. The wave height transducer was attached to the carriage 21 feet forward of the model's at-rest

longitudinal center of buoyancy location.

The restraint ropes were manually controlled to accelerate and decelerate the model with the carriage. They were left slack while the carriage was moving at constant velocity and data were being collected, The safety ropes were adjusted to prevent the model from contacting the carriage or putting tension on.the unbilical cable. Any run during which the safety ropes were loaded was voided. The umbilical cables remained slack at all times. Hence,

the model was free to move in all degrees of freedom while data were b,eing collected.

During data collection, the lateral position of the model was, as implied above, maintained by a rudder control servomechanism dtiven by sway and yaw signals. Longitudinal position was maintained by manual control of model power. The safety ropes prevented excessive model excursions in the event of failures

in either position control system.

A video tape was made of the data collection portion of each run. After each run, the strip chart records, video records, and harmonic analysis results were examined. Working plots of pitch, heave and relative motion were updated

if the run was judged to be valid.

APPENDIX B

PROBABiLITY Øf DECK IMMERSION

t the present state-of-the-rt,. predictions of deck wetness are lini;d o cases of deck Immersion, i..,wetness resulting from deformation of.

incident waves (as observed tooccur during the fishing vessel experiment) is

not predictable. Reference 5 formuFetes the probability of deck immersion per cycle of random wave encounter, P, at a specified location as

whereF is the freeboard at the location under consideration and a Is the standard deviation of relative motion at the same location. This formulation Indicates that P is exponentially proportional to the squares of both F and a; and hence, that minor errors in either of these parameters can cause P to

be significantly in error. Further, it Is evident that a fortuitous combination of errors in F and a could produce a correct ratio of F to a, and thus give a misleading impression as to the validity of the formula. In view of these factors, evaluations based on equation (Bl) require that F and a be very care-fully defined; and that their effects on P be considered separately as well as jointly.

The standard deviation of relative motion, a In equation (Bl), must, in the absence of measurements in random waves, be obtained from linear super-position as a2 c

(A)2

A

Sdw

0

where (rA/CA)2 is the response amplitude operator.of relative motion, S is the wave spectrum of Interest, and w is wave frequency. Response amplitude

operators computed using strip theory may be used to compute a theoretical value of a, say aT. A curve faired through measured response amplitude

operators is used to obtain a corresponding experimental value, aE. When the

19

experimental results Indicate nonlinearity, aE Is not rigorously defined; but may be considered to vary with wave slope for exploratory purposes. The theo-retical and experimental values of a should, of course, be computed using the same wave spectrum. Selection of an appropriate wave spectrum isdifficult because equation (B2), and hence equation (BI), is sensitive to both the total energy and shape of the spectturn.

Theoretical and experimental values may also be associated with freeboard (F In equation (61)). Theoretical freeboard is read from the vessel's load waterline while experimental freeboard accounts for the influence of trim and

sinkage. (It would also be possible to attempt to account for the vessel's own wave system in defining experimental freeboard. However, procedures for handling this matter In the presence of possible dynamic ef.fects are not clear;

so consideration will be limited to trim and sinkage.*) Assuming that the ves*l trims about its longitudinal center of buoyancy (LCB), experimental

freeboard, FE, can be related to theoretical freeboard, FT. as

FE = FT + ZO + I tan (B3)

where is sinkage taken negative down, I is the distance from the LCB to the locatin under consideration taken positive forward of the LCB, and is trim angle taken positive when bow-up.

The foregoing considerations indicate the desirability of comparing a theoretical probability of deck immersion

F

= e'a.1)

with an ex,perlmental probability of deck immersion

F

(E)2

= e

*The Appendix C material is relevant here. Evidently the wave profile could have been treated s static phenomenon independent of dynamic swell-up and

incident wave distortion.

20

(64)

for aT aE a but FT FE, for FT = FE F but a1 aE for variable nonlinear cases, and for combinations of these error sources.

For the fishing vessel, theoretical freeboards, FT$ were read from the load waterline to sheer.* Thus, the fo'c'sle deck extends slightly above the forward F11s, and F1 at Station 5.2 is to the top of the bulwark. An argument could be made for taking freeboard to the edge of the fo'c'sle deck at the forward locations and to the edge of the main deck at Station 5.2, but it was felt that freeboards to sheer would serve as well as any for exploratory purposes.

Trim and sinkage data measured in calm water (see Figure 24 of the text) were used to define experimental freeboards. In this context, it should be noted that trim and sinkage measurements obtained in low waves were marginally

higher than those obtained in calm water; and that some scatter and/or dependence on incident wave characteristics was observed in steep waves.' However, trim and sinkage in waves had to be established on the basis of the zero-shifts of oscillatory time histories. Hence, the calm water data were considered to be more definitive.

Theoretical response amplitude operators were taken from the YF 17 (strip theory) results. Experimental response amplitude operators for general use were faired from the experimental data to represent mean wave steepness in nonlinear cases (Stations 0.0 and 1.0 at 10 and 15 knots), experimental

response amplitude operators were also faired for low waves (steepness on the order of 1/90) and for high waves (steepness of 1/40 to 1/30).

For the initial exploration, it was decided to limit consideration to a single wave spectrum. A Pierson-Moskowitz spectrum, reference 6, representing waves of 10-foot significant height was selected. This spectrum increased

monotonically over the frequency range In which the experimental and theoretical response amplitude operators peaked. However, it had sufficient energy in the range of significant relative motion to ensure that deck immersion probabilities large enough to be of practical concern would occur.

Integrations required to obtain aT and _aE for the combinations of response amplitude operators and wave spectrum just defined (see equation B2) were

approximated numerically. A wave frequency range from 0.8 to 2.0 radians per second was considered. Slight extrapolations of the response amplitude operator curves were made when required to obtain values at the extremes of the cited frequency range.

The following cases were explored in detail:

aT=cJE

abut FTFEI

FT=FE=FbutaTaE, and

a.. a and F1. FE.

When needed, aE was established on the basis of the general use experimental response amplitude operator described above. Comparisons were made in terms of the ratio

-

.1. ((T)2

(E)2]

pI=exP

2 _aT

derived from equations (84) and (B5). The results of these comparisons are presented in Table Bl.

For the first case, a was taken to be equat to aT because a1. was usually higher than aE and would thus produce larger probabilities. For the second case,

F was taken to equal FE. This decision was predicated upon the fact that the initial case had indicated that freeboard errors alone could cause T'E to depart significantly from unity. Such being the case, it appeared that obtaining useful results from strip theory/linear superposition predictions would almost certainly require that trim and sinkage be accounted for in establishing free-board. The trim and sinkage data necessary for a "hybrid" approach using FE and

aT should, in some instances,+be'obtalflable from resistance series data bases. Potential fallacies associated with simultaneous consideration of errors from

two sources are illustrated by the third case presented in Table Bi.

The hybrid case, for which F ₌ FE and = a1, is considered to be the most relevant of the predictive methods considered. Focusing attention on the Table Bl results applicable to this case, it is seen that the 10-knot condition indi-cates some potential for obtaining conservative estimates of deck immersion

(B6)

probabilities over the forward quarter. However, two of the locations Involved have±non1iner relative motion characteristics, At Station 0.0, aE varies from 3.5 feet In low wves to 4.3 feet in high waves, The corresponsing figures for Stat Ion 1.0 re 3.2 arid 3.6 feet. Hence, P /P may actually vary from 1.3 to 3.5at Station 0.0 and fro 1. to 1.9 at Station 1.0.

The 15-knot ratios (still In reference to the hybrid case) are obviously too far from unity to be of any practical value. At 5 knots, the ratIos are erratic; and some, considering the ract that the qualitative agreement between strip theory and experiment was best for this condition, are surprisingly high with respect to the 10-knot ratios. It was felt that the high ratios at 5

knots might be due in part to the fact that the absolute probabilities associated with this condition were generally lower than those at 10 knots. To validate this hypothesis, a wave spectrum with the same significant height -(10-feet) used for the preceding oomputatlons, but with Its modal frequency

shifted to a higher value, was applied to the 5-knot response amplitude

operators. The resultant values of T'E were 1.3, 1.0, 0.7 and 1.5 in order of increasing Station number. So, the ratios were generally closer to unity, but continued to be nonconservative in way of the forward quarter point. This nonconservatism may be attributed to the fact that the kinematic definition of

relative motion was uncommonly deficient for 5 knots at Station 2.5 (see Figure 8 of the text).

The results of the exploratory investigation and minor extensions just described gave no indication that deck Imersion probabilities which were viable over a significant range of speeds and/or locations could be obtained from strip theory predictions for the fishing vessel. Local instances of

near-validity can, of course, be found within the matrix of locations, vesse1.:, speeds, error source combinations, and wave spectral characteristics availab1 fr consideration. However, the likelihood of obtaining results of general utility appeared too remote to justify further effort. The investigation of deck irmersion probabilities Was accordingly terminated.

(Intentionally blank)

24

-c---APPENDIX C

PURIFiER CONSIDERATIONS REGARDING RELATIVE MOTION

Subsequent to drafing this report, the first author had occasion _to

conduct a literature survey regarding abovewater bow phenomena, _{Two documents} relevant to the difflcultjes _{re?orted here In interpreting relative motion were}

located. _{In reference 7, TaeIçi describes forced oscillation experiments}

with several ship models. These experiments indicated that relative motion was influenced by waves produced by the oscillations of the models. _Tasakicalled this phenomenon dynamic swell7upr" In reference 8, van Sluljs describes an experiment In which a restrained Ship model was towed In waves. This experiment

Indicated that Incident wave distortion influenced _{relative motion. As was the} case here, van Sluijs found that reTative motion transfer functions based _{on a} farfleld wave measurement did not converge to unity with Increasing encounter frequency. However, van Sluijs did obtain convergence _{to unity in terms of the} 'distorted incident waves.

It Is thought that these results both support the findings of _{the fishing} boat Investigation and emphasize the need for further _{research In this area.} Dynamic swell-up and incident wave distortion likely account for _{at least a} portion of the discrepancies found to exist between measured relative motion and relative motion as computed from measured pitch and _{heave using the} kine-matic definition. Since Tasaki's results were applicable _{to high-block hulls} while van Sluijs considered a fine, military hull, It _{is evidently correct to} state that deficiencies in the kinematic definition of relative motion are common to many types of hulls. _{Thus, a more extensive analysis of the relative} motion data obtained during the fishing boat experiment _{could advance the}

general state-of-the-art regarding predictions of deck wetness,

In the general case, it appears that relative motion _{should be thought} of in terms of three components:

A kinematic component defined to be the victor sum of absolute ship motion and undistorted Incident wave motion,

A dynamic swell-up component introduced by oscillations _{of the hull} at the free surface, and

3. An incident wave distortion component caused by the fact that the

presence of the hull modifies the incident waves.

in this context, the YF 17 predictions of relative motion presented here represent only the kinematic component; and are based on strip theory predic-tions of pitch, heave, and their phases with respect to the (undistorted) incident waves. On the other hand, the experimental data on relativemotion reported here encompass all three components. The relative motion computations performed to illustrate the inadequacy of the kinematic definition thereof (shown as open circles in the relative motion figures of the text) apply, like the YF 17 predictions, only to the kinematic component of relative motion. How-ever, they are based on measured pitch, heave, and phases rather than on strip

theory predictions of these variables as in the case of the YF 17 results. Thus, the differences between the results of these computations and the experimental data are direct measures of the deficiencies of the kinematic definition of

relative motion. The differences between the YF 17 and experimental results for relative motion, on the other hand, indicate the combined effect of deficiencies in both strip theory and the kinematic definition of relative motion. it

follows that the T'E ratios given in Appendix B also include the effects of both strip theory and kinematic definition errors.

For completeness in treating the generalized deck wetness problem, it also needs to be pointed out that freeboard, like relative motion, should be con-sidered in terms of several components. These are:

A geometric component measured vertically from the load waterline to the weather deck, bulwark top, or whatever point appears most logical for the particular vessel and location under consideration,

A ship's own wave system component associated with the static (or near-static) swell-up of water alongside the hull,

A change in level component resulting from trim and sinkage, and A shape component indicative of effective changes in geometric

freeboard brought about by knuckles, flare, or other features of above-water, bow design.

It will be noted that these components, in contrast to those listed for relative motion, are all static or nearly so. The first and fourth components are

functions of hull geometry alone while the second and third are functions of geometry and ship speed. The presence of incident waves may have some Impact on the ship's own wave system and change of level components, but

these components do not appear to differ radically from their calm water values at glvàn speed. Unfortunately, the "shape component" cannot, be quantitatively evaluated at the current state-of-theart.

in the context of Appendix B of this report, the theoretical freeboards, F1, reflect

only

the geometric component of freeboard while the experimental

freebeards, ref léct the geometric and change of level components. On the basis of the foregoing conwnets, it appears that the ship's own wave system component covid have been incorporated into the experimental freeboards. When

the analysis was performed, however, the distinctions between the static and dynamic components involved in the problem were not clear. it can be observed frm Figures 24A and 24B Qf the text that incorporating this component would have Produced mixed 'changes In the comparisons between F1 and FE.

It Oppears possible that including or omitting the ship's own wave system component may provide a rough indication of degree of wetness. The underlying

(and unproven) hypothesis is that a condition in which only the ship's own wave system'rtSe. above the weather deck will cause less severe wetness than one In which theother factors involved cause water to rise above the weather deck. Coøditions of'the former type might be identified with "heavy spray" while conditions f't.he latter type are identified with "shipment of green water."

Frmthi

viewpoint, careful examination of the assumptions underlying state-of-th.-.rt statistical formulations for deck wetness probabilities seems in order when they are used with the ship's own wave system freeboard component.

REFERENCES

Korvin-Kroukovsky, B.V., "Investigation of Ship Motions In Regular Waves," Trans. SNAME, Vol. 63, 1955.

St. Denis, M. and W.J Pierson, "On the Motions of Ships In Confused Seas," Trans. SNAME, Vol. 61, 1953.

Frank, W. and N. Salvesen, "The Frank Close-Fit Ship-Motion Computer Program," NSRDC Report 3289, June 1970.

Hubble, E.N. and J.B. Hadler, "Prediction of Ship Motions in Regular and Irregular Head Waves," NSRDC Report SPD-623-01, April 1975.

Ochi, M.K., "Extreme Behavior of a Ship in Rough Seas--Slaming and Shipping of Green Water," Trans. SNAME, Vol. 72, 1964.

PIerson, W.J. and L. Moskowitz, "A Proposed Spectral Form for Fully Developed Wind Seas Based on the Similarity Theory of S. A. Kitalgorodskii," NYU

College of Engineering, Research Division, 1963.

Tasaki, R., "On the Shipping Water in Head Waves," Jour. ZK Vol. 107, July _1960.

van Sluijs, M.F., "Ship Relative Motions and Related Phenomena," Symposium on the Dyramcs of Marine Vehicles and Structures in Waves, University College, London, April 1974.

rAitE 1

- BALLAST CONDITIOK FOR.THE FISHING VESSEL

rmeter

¶

Spec1f.Tcaion

YF-17 _Pre

Experiment

_Post

Average

398 396 395 4OO 398

a 12.62 12 62

12,5 + 0 3

12 5 + 0 3

12.5 + 0 3

TS&

1;a:

14.8

14.5 +0.3

146 +0.3

14.6 + Q.3

TABLE B1 - DECK IMMERSION PROBABILITY DATA 30 V

(knots)

Station

I

(feet)

F E

(feet)

a T

(feet)

a E

(feet)

.FT, F

_{a a1}

a1, a

F' _FE

aT, a

FT, FE

5

0.0

9.0

8.8

3.6

3.0

0.9

3.7

3.2

5

1.0

7.1

6.9

2,9

2.8

0.9

1.2

1.0

5

2.5

5.3

5.1

1.9

2.2

0.8

0.

0.3

5

5.2

11.0

3.8

1.1

1.0

0.5

3.5

1.8

10

0.0

9.0

8.5

11.6

_3.9

0.8

_1.9

1.6

10

1.0

7.1

6.6

3.8

3.4

0.8

1.5

'1.1 10

_2.5

5.3

4.7

2.9

2.7

0.7

1.2

0.9

10

5.2

4.0

3.3

2.0

2.3

0.5

0.7

0.4

15

0.0

9.0

10.2

5.6

4.1 1.11

4.3

6.1 15

1.0

7.1

7.8

11.8 3.1

1.2

6.2

7.9

15

2.5

5.3

5.2

3.8

2.5

1.0

3.4

4.0

15

5.2

4.0

2.5

2.9

2.3

0.6

1.2

0.7.

SHEER & BULWARK TOP

POOP DECK

MAIN DECK\

6'

3'

3'

Figure 1

-Body Plan of Vessel Investigated

FO'CS'LE DECK

-LOWER KNUCKEL I9.

I

-14'

POOP DECK

-FREEING PORTS MAIN DECK

++ ---±---±--±-

-H--±

+14 +10

- +6

BL 10.0 8.0

60

5.2 5.0

40

3.0 2.5 2.0

10

00

*

* * *

Figure 2 - Profile of Vessel Investigaftd

SHEER & BULWARK TOP

(4 'A 3.

00L

0.0 t 1.0

-

DELFr)

- STRIP THEORY (YF17)

.1. EXPERIMENT.

F-5 KNOTS

-

2.Cfl

1.0

- :.

(-t-R

L -

EL1T'J

STRIPTHEORY(YF17}

EXPERIMENT:

Figure 4

Heave a 5 Knots

314

4.0

40

I

KNOTS

3.0

2.0 X! L 0.0k

0.0

1.0

+ 1001 0

100

+

.1R

-

STRIP TH EXPERM Zç 60

I

160

0.5

tO

1.5

rNdy Eii

L. - ILF1J

EORY WF17) ENT

4

1 5 KNOTS 1.5 2.0

2.5 4.- ----.Q

3.5

-7-Figure 5

-

Pitch-u-Wae and Heae-t-Wae Phases

ai Knots

-5 KNOTS

20

2.5

3.0 3.5 XI L 0.5

10

-r

_-L

*T201 TRqL -

tLFj

STRIP THEORY (YF7)

!XPERMENT

KNEMAT1C COMPUTAT iON

4

/

-0,0

10

2.0

3.0

4.0

-i p moij CTL CL

FT)

STRIP THEORY (YF17) EXPERIMENT

0

KINEMATIC COMPUTATION

37

0.0 1.0 2.0

3.0

₄₀

X/L

'A 4.0

-*S11IP T1-1B'RY

STRIP THEORY (YF17)

I]

EXPERIMENT

0

KINEMATIC COMPUTATION

3.0---f

TIT

.11

2.0

0

O

1.0 çJ;)

/

1.0

2.0

30

4.0

! L

Figure 8

Station 2.5 Relative Motion at 5 Knots

38

5 KNOTS

STA. 2.5

0.0 0.0

rA

- 2.0

A 1.0 0.0 0.0

STR'P TDy (TRL--

LPT

STRIP THEORY (YF17)

I

EXPERIMENT S

o KINEMATIC COMPUTATION

4.0 I

5KNOTS

STA.5.2

39

4.0

20L

1.0

C

L_ELFj

-

STRIP THEORY (YF17) EXPERIMENT

4

7

Fitwe JO - Pitch a

10 Knots

4.0 3.0 2.0 1.0 0.0 0.0

s-r

ThoW (TR

t

-STRIP THEORY (YF17)

I

EXPERIMENT

I

10 KNOTS

H

1 -J 1.0

2.0

3.0

4.0

Figure I I - Heave at 10 Knots

+100 E0ç ₀ :...100

05

.,4_ STRP tW'R':I

T

r)

SFRiPTH&W(T1F17)

TEXPER!MENT

.

_a +40

oO.

13

20

2.5 3.0

i_-

i_-

+--

+---42

20

2.5

3.0.

35.

1-igure 1 2

Pitch-to--%ae and Hae-to-Wae Phases at 10 Knots

10 KNOTS

rA

5.0

4.0

3.

2.0

1.0

0.0

- 4SrRIp ThE

(TtAL- L)

STRIP THEORY (YF17)

I

EXPERIMENT

.0 KINEMATIC COMPUTATION

.0.0

1.0

2O

30

4.0

?iL

5.0 4.0 2.0

1.0

h----0.0

00

-4-.

rR

ra4oy\ (-rL

Lrr)

STRIP THEORY (YF17)

I EXPERIMENT

O KINEMATIC COMPUTATION

I 10 KNOTS STA. 1

0

1.0

20

3.0

4.0

X/L

Figure 14

Station I 0 Relative Motion at 10 Knots

rA 5.0 4.0 3.0 2.0 1.0 0.0

sr pn.to

(rR L.

b

LFTJ

STRIP THEORY (YF17)

i }EXPERIMENT

Q KINEMATIC COMPUTATION

"5

10 KNOTS STA. 2.5

00

1.0 2.0 3.0

₄₀

IL

rA 4.'J 3.0 1.0

(ILLF1)

STRIPTHEORY (YFI7)

I

EXPERIMENT

0

KiNEMATIC COMPUTATION 46

I

10KNOTS1

ST&5.2.

H-f:.

0.0

1.O

2.0

3.0

4.0

Figre 16.- Station 5.2 Relative Moiwn at 10 knots

2.

4.0

0L

0.01

0.0

4-

St1P

4EoR CLDLP7j

STRIP THEORY (YFI7)

T

EXPERIMENT

-r

1.0 2.0

3.0

FgL3re I 7 -. Pitch t I S Kiiots

L7

1 5 KNOTS

LA 4.0

3.0H----4

2.0

1,0k.

co

0.0 1.0

-*---srt P fl-4c

_{CTR L _tPt)}

- STRIP THEORY (YF17)

EXPERMENT 2.0 .' . i-\/ L. !

S -

at I

Kw

15 KNOTS

+ 100 0 ezc

100

0.5 1.0

1.l+lb

rEip m

(TL-- STRPTHEORV(Y7'P'

+4O

60

15

20

X/L f..

25

30

A

f

I

260L..

I

L

..L

05

₁₀

1.5 2.0 2.5 3.0

₃₅

4

AlL

Figure 19 - Pitch-toWave and Heave-t-%'Va

Phases at S Knots

/

3.5

4

-I 15 KNOTS

H

SI

I

I

.

--

_i

:

15 KNOTS

rA

6.0

4.0

2.0

4-u -rp

(TL D ELTJ

STRIP THEORY (YF17)

I

EXPERIMENT

Q

KINEMATIC COMPUTATION

J__

00

1.0 -I--T

F&gure 20

Stat,n l.0 Reiatis'e MoUen at 15 Knots

50 15 KNOTS STA. 0 0

O

-.

J

2.0

30

4.0

6.Or

.+-

S-rRP T4E&Y

(2L -D

rj

- STRIP THEORY (YF17)

i 1EXPERIMENT

0 KINEMATIC COMPUTATION

1 15 KNOTS

STA.i

5.Ob

4

-

4.0--rA

TL.4T!

2.0E---fJ-00

1.0

I

2.0

3M

4.0

F:

3.0

'A

-

4ST1P T44t

Ot

(.TRL -t EtFTJ

- STRIP THEORY {YF17)

I

EXPERIMENT

O KMATIC COMPUTATION

T 15KNOTS

STA.2.5

0.0

1.0

20

3.0

40

XIL

6.0

-

--sTc2P

A1.-otp

STRIP THEORY (YF17)

I

EXPERIMENT

.

0

KINEMATIC COMPUTATION

4.0-2.0 0.0 0.0 1.0 15 KNOTS 53 STA. 5.2

-Figure 23 - Station S.2 1iatie Motion at 15 Knots

2.0

3.0

40

POOP DECK

V OKTS

= Zr,) 0 I

BULWARK :

\

_\

\

-.

MEASURED WAVE PROFILE

WAVE PROFILE INFERRED FROM MEASURED PROFILE (VERTICAL SCALE EXAGGERATED)

MAIN DECK

/

/

I 94 FO'CIS'LE DECK

Figure 24A -

Catm Water Trim, Sinkage. and Wave Profile

at 0 and S knots.

/

V 10 KTS = +0.3 DEC Z0

= -0.7 FT.

V 15 KTS

;+35 DEG

Z= -1.5 FT.

MEASUREDWAVE PROFILE

WAVE PROFILE INFERRED FROM MEASURED PROFILE WAVE PROFiLE FROM VDEO RECORDS

(VERTICAL SCALE EXAGGERATED)

---ff.i: r;

_t.j i'I.

-'-,' -I.

kL:

o

V=5KNOTS,

.'_1/F

-0

V=1OKNOTS

2.00

(

V=I5KNOTS,

?JL =

250

8

,to

4--...

-

-

.----

--4--//

Fgu' 25 - Pitch Amtiuide Linari

56

ZA

o V=5KNOTS,

1L=i.75

O V=1OKNOTS,

X/L=2M0

4 r _{v = 15 KNOTS,}

X/L=2.50

2

-hut 26

Hea%eArnphtUdI Liiicarit

57

/

12 V. 5 KNOTS X/L 1.50

fl.STA.00

STA.1.0

10 _{STA. 2.5}

sTA.5.4

8 -if 58

Figure 27

Relaiive Motion Linearity

t 5 I<.nos and X!L 1 .50

-J

12

V = 10 KNOTS

X/L 1.75

o STA. 0.0

STA. 1.0

STA2.5

o STA. 5.4

2 0 -F 1 2

0

i

j

FiQure 28

Relathe \Iotion Linearily at 10 Knots and AlL

.75

12 10 8 6 2

0

60

V= 15 KNOTS

X/L=2.38

o STA.O.0

STA.1.0

STA.25

O

STA. 54

0

I

-t

o

A

_1

_____

0

1 2

3 rA 2 V=1O KNOTS

\/L

1.25

o STA. 0.0

STA.1.0 STA. 2.5

O STA.5,4

1 a 0.0 4-.

--...-I..-..

-I

a,

+ -1 I

i

0.5

10

15

Finre 30 - Reanve M,tion linearity al

0 Knots and X/L

1.25

r

_{ANALOG TO}

DIGITAL

CONVERTER

11

,,-(DIGITAL'

TAPE

/ HARMONIC

( ANALYSIS

\SO FT WARE / REDUCED DATA \TRANSDUCE R SUPPORTING ELECTROMCS KEYBOARD DIRECTIVES I MtCROPHONE / It [RUDDER CONTROL STRIP CHARTS

I VIDEO/

AUDIO (PLAYBACK)

(ANALOG\

TAPE

₎

SPECIAL EFFECTS UNIT (PLAYBACK)

Figure A! - Flow Chart of Instrurnentatioi System

62

\ CAMERAS

\

\